1. Field of the Invention
The present invention relates to stable polymer polyols produced without the use of a preformed macromonomer stabilizer. In particular, the instant invention relates to the in situ polymerization of two or more monomers in a polyol blend wherein at least one monomer is a bifunctional isocyanate compound containing both an isocyanate group and an ethylenically unsaturated group and wherein the polyol blend contains a base polyol and an amine terminated polyether which is more reactive with the bifunctional isocyanate compound than is the base polyol.
2. Description of the Prior Art
Polymer/polyol compositions suitable for use in producing polyurethane foams, elastomers and the like are known materials. The basic patents in the field are Stamberger U.S. Pat. No. Re. 28,715 (reissue of U.S. Pat. No. 3,383,351) and U.S. Pat. No. Re. 29,118 (reissue of U.S. Pat. No. 3,304,273). Such compositions can be produced by polymerizing one or more ethylenically unsaturated monomers dissolved or dispersed in a polyol in the presence of a free radical catalyst to form a stable dispersion of polymer particles in the polyol. These polymer/polyol compositions have the valuable property of imparting to polyurethane foams and elastomers produced therefrom higher load-bearing properties than are provided by the corresponding unmodified polyols.
The polymer/polyol compositions that found initial commercial acceptance were primarily compositions produced using acrylonitrile. Many of these compositions were somewhat higher in viscosity than desired in some applications. More recently, polymer/polyol compositions produced from acrylonitrile-styrene monomer mixtures have been used commercially.
Polyurethane foams made with polymer/polyols are widely utilized. The two major types of foam are generally termed slabstock and molded. More particularly, slabstock foams employing polymer/polyol compositions are used in the carpet, furniture and bedding industries. One primary use of slabstock foam is as carpet underlay.
In the molded foam area, the primary type of foam employed is generally termed high resiliency (HR) molded foam. HR molded foams have been widely used in the automotive industry for applications ranging from molded seats to energy-absorbing padding and the like.
The wide demand for polymer/polyols has spawned a number of trends that have created the need for additional technology. For example, the general trend is to provide slabstock foams that are virtually scorch-free, i.e., white foam products. Indeed, the desire is to provide techniques capable of producing, without substantial economic penalty, virtually scorch-free foams at ever-decreasing densities (viz. 1.5 pounds per cubic foot or less) while maintaining satisfactory load-bearing and other foam properties.
Such scorch-free foams have been obtained by utilizing relatively high styrene contents (e.g. - about 65 to 70 percent styrene) in the acrylonitrile styrene monomer mixture. The utilization of such high styrene monomer mixtures in the molded foam area is also widespread.
The preparation of polymer/polyols from such high styrene monomer mixtures has created difficulties. More particularly, such difficulties arise due to the state of the art to which polyurethane production has now advanced, such as the degree of the stability of polymer/polyol compositions. Many applications require somewhat rigorous stability characteristics, and such characteristics become more difficult to achieve when high styrene monomer mixtures are employed.
A further trend is the desire to provide foams with ever increasing load-bearing characteristics for many applications. This is particularly prevalent in the slabstock area where many formulations require the use of "neat" polymer/polyols, i.e., the polymer/polyol is employed without dilution with conventional polyols. While typically not used neat in the molded foam area, polymer/polyols capable of imparting higher and higher load-bearing characteristics to such foams are likewise desired.
Such increased load-bearing characteristics are being obtained by increasing the polymer or solids content of the polymer/polyol. Solids contents of 35 to 50 weight percent or even more are accordingly desired. Preparing such high solids content polymer/polyols with the degree of stability often desired becomes substantially more difficult as the solids content is increased.
The trend toward the use of high styrene monomer mixtures and high solids content polymer/polyols has likewise resulted in polymer/polyols sometimes having higher than desired viscosities. The viscosity of a polymer/polyol must, of course, be sufficiently low to allow ease in handling during manufacture. Moreover, the viscosity must allow ready transport, handling and, ultimately, adequate processability in the foam processing equipment being utilized. The viscosity level is becoming of acute concern in the molded area due to the sophisticated mixing systems, such as impingement systems, that are increasingly being utilized. There is a clear need to provide the desired polymer/polyols with as low a viscosity as possible.
Also, the degree of stability of the polymer/polyol, as alluded to previously, is of concern. At one time, there was not much concern for the seediness or filterability of polymer/polyols in actual commercial practice. However, the state of the art of polyurethane production has now advanced to the point where these considerations are very important in many applications. This is particularly important in the molded foam area.
Thus, the development of sophisticated, high speed and large volume equipment, machines and systems for handling, mixing and reacting polyurethane-forming ingredients has created the need for highly stable and low viscosity polymer/polyols. Polymer/polyols must accordingly meet certain minimum requirements in order to be capable of being satisfactorily processed in the sophisticated foam equipment now used. Typically, the prime requirement is that the polymer/polyols possess sufficiently small particles so that filters, pumps and the like do not become plugged or fouled in relatively short periods of time.
Since the basic development by Stamberger, a substantial amount of effort has been devoted to providing improved polymer/polyols and to improved preparation techniques. For example, U.S. Pat. No. 4,208,314 to Priest et al. discloses low viscosity polymer/polyols made from acrylonitrile-styrene monomer mixtures. These polymer/polyols can be converted to low density, water-blown polyurethane foams having reduced scorch, especially when the acrylonitrile to-styrene ratio is relatively low. The Priest et al. patent also provides a process for making polymer/polyols whereby the particulate nature of the polymer portion of the product is considerably improved, compared to polymer/polyols prepared by prior processes. The improved process provided by Priest et al. includes, in general, maintaining a low monomer to polyol concentration throughout the reaction mixture during the polymerization.
A further improvement in the formation of polymer/polyols is provided by U.S. Pat. No. 4,148,840 to Shah. This discloses a process for producing highly stable and filterable polymer/polyol compositions by polymerizing the monomer or monomers in situ in a polyol mixture that includes a minor amount of preformed polymer/polyol.
It has been recognized that the stability of polymer/polyols requires the presence of a minor amount of a graft or addition copolymer which is formed in situ from growing polymer chains and polyol molecules. Some prior approaches have thus been directed to incorporation of small amounts of unsaturation into the polyol in addition to that inherently present in the polyoxyalkylene polyols typically used in forming polymer/polyols in the belief that improved stability will result due to an increased amount of an addition copolymer stabilizer expected to be formed. U.S. Pat. Nos. 3,652,639, 3,823,201, and 3,850,861, British Patent No. 1,126,025 and Japanese Patent Nos. 52-80919 and 48,101494 all utilize this approach.
In a similar vein, the use of what may be termed "stabilizer precursors" has been proposed. More specifically, the concept is to carry out the preparation of the polymer/polyol in the presence of a suitable amount of the stabilizer precursor, which precursor comprises what has been termed a "macromer" that contains a particular level of reactive unsaturation. The belief is that, during polymerization in the preparation of the polymer/polyol, adequate amounts of stabilizer will be formed by the addition polymerization of the precursor stabilizer with a growing polymer chain. The concept of using stabilizer precursors in polymerization is a well-recognized and old technique as discussed in "Dispersion Polymerization in Organic Media", edited by K. E. J. Barrett, John Wiley & Sons, copyright 1975. U.S. Pat. Nos. 4,454,255 and 4,458,038 are recent examples utilizing this technique. The macromer in the '255 and '038 patents may be obtained by reacting a polyol with a compound having reactive ethylenic unsaturation such as, for example, maleic anhydride or fumaric acid. A further example of the use of this technique is U.S. Pat. No. 4,460,715. The reactive unsaturation in the '715 stabilizer is provided by an acrylate or methacrylate moiety.
More recently, U.S. Pat. No. 4,550,194 disclosed a polyol which is alleged to find utility as a precursor in the preparation of graft polymer dispersions although no specific mention of its use to prepare a stabilizer is made. This polyol is prepared by reacting a conventional polyether polyol with an organic compound having ethylenic unsaturation and an anhydride group forming a half ester and subsequently reacting that product with alkylene oxide in the presence of calcium naphthenate or cobalt naphthenate. In particular, see example 51 of this patent where pentaerythritol is used.
In U.S. Pat. No. 4,652,589, stabilizer precursors are taught for polymer/polyols. In particular, Stabilizers A and B utilized polyols with added unsaturation.
In addition, U.S. Pat. No. 4,390,645 discloses a stabilizer made from a polyanl and isocyantoethylmethacrylate.